Battery life extending technique for mobile wireless applications using bias level control

ABSTRACT

An operating voltage applied to a transmitter&#39;s power amplifier in a mobile wireless transceiver is dynamically controlled so as to improve the efficiency of the transmitter at all output power levels. In one embodiment, the bias current levels within the transmitter are also varied to optimize the efficiency of the transmitter at all output power levels. In a preferred embodiment, a highly efficient switching regulator is controlled by a control circuit to adjust the operating voltage and/or bias current for the power amplifier in the transmitter. The control circuit has as its input any of a variety of signals which reflect the actual output power of the transmitter, the desired output power, or the output voltage swing of the transmitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.08/843,107, entitled “Battery Life Extending Technique For MobileWireless Applications,” incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to wireless transmitters and, inparticular, to a technique for extending the battery life in such atransmitter.

BACKGROUND

[0003] Extending battery life is a key concern for users andmanufacturers of cellular telephones and other portable transceivers. Apowerful signal generated and transmitted by the wireless transceiverdraws more power from the battery than when a lower power signal isgenerated and transmitted. Accordingly, a number of prior art techniqueshave been employed to adjust the gain of a portable transmitter so as tonot transmit a signal more powerful than necessary for adequatecommunications. Examples of such ways of automatically adjusting theoutput power level of a transmitter are described in U.S. Pat. Nos.4,760,347, 5,129,098, and 5,446,756, incorporated herein by reference.

[0004] Although the prior art techniques selectively reduce the outputpower of the transmitter, the efficiency of the transmitter is notimproved by the prior art methods. The transmitter is typically biased,and operating voltages are set, so that the transmitter output signalwill not distort in an adverse way at the highest expected outputsignals. These worse case operating conditions can draw significantpower from the battery even when no signal is being transmitted. Suchworst case operating conditions are not required when the transmitter isnot transmitting its maximum signal. Hence, the transmitter's efficiencyis lower when transmitting lower power output signals. A lowerefficiency equates to wasting battery power, reducing talk time.

[0005] What is needed is a technique for extending the battery life inmobile wireless applications.

SUMMARY

[0006] A technique is described herein which dynamically reduces theoperating voltage applied to a transmitter's power amplifier in a mobilewireless transceiver so as to increase the efficiency of the transmitterwhen the transmitter is not outputting its maximum output power. Thus,the total power consumption of the transmitter is reduced as compared toprior art transmitters. In another embodiment, the bias voltage or biascurrent levels within the transmitter are also varied to optimize theefficiency of the transmitter at a particular output power level. Thistechnique of controlling the transmitter's operating voltage and biasvoltage/current may be used in conjunction with conventional techniquesfor automatically reducing the gain of the transmitter.

[0007] In a preferred embodiment, a highly efficient switching regulatoris controlled by a control circuit to adjust the operating voltage andbias voltage/current for the power amplifier in the transmitter. Thecontrol circuit has as its input any of a variety of signals whichreflect the actual output of the transmitter or the desired output powerof the transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a block diagram of the basic components of a transmittersection in a wireless transceiver incorporating one embodiment of thepresent invention.

[0009]FIGS. 2-6 illustrate various embodiments of controllers forcontrolling an output of a voltage regulator for application to a poweramplifier in a wireless transceiver.

[0010]FIG. 7 illustrates one embodiment of a controller for controllingan output voltage of a voltage regulator for application to a receiverin a wireless transceiver.

[0011]FIGS. 8 and 9 illustrate a conventional buck type regulator and aboost type regulator, respectively.

[0012]FIG. 10 illustrates one embodiment of a power amplifier which hasits efficiency improved using the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]FIG. 1 illustrates a power amplifier 10 for a transmitter 11 whoseoperating voltage Vdd is provided by a variable voltage regulator 12.The output voltage Vdd of regulator 12 is controlled by a signal from acontroller 14 applied to a control terminal 13. A battery 15 suppliespower to regulator 12.

[0014] Controller 14 receives a signal at an input terminal 16 whichsignifies the actual output power of the power amplifier 10, the desiredoutput power of amplifier 10, or a measure of the output voltage swingof amplifier 10. Controller 14 then sets, based on this input signal,the output voltage Vdd of regulator 12 such that amplifier 10 willoperate under its most efficient conditions for the particular outputpower level.

[0015] Controller 14 also, optionally, provides a bias voltage or biascurrent control signal to amplifier 10 via line 20 to adjust the biascurrent or voltage levels in amplifier 10 for optimum efficiency at aparticular output power level.

[0016] When amplifier 10 is outputting its maximum power level, theoutput voltage Vpa swing of amplifier 10 is a maximum, and amplifier 10operates with relatively high efficiency. The various transistors andother components in amplifier 10 are biased and otherwise operated so asnot to introduce significant distortion into the output signal. As theoutput power is reduced, the output voltage swing and current drawn frombattery 15 are reduced. In accordance with one embodiment of theinvention, because of the reduced output voltage swing, the operatingvoltage Vdd provided to amplifier 10 by regulator 12 is reduced, withoutintroducing distortion, to save additional power.

[0017] Further, in accordance with one embodiment of the invention, asthe power output level is reduced, the bias voltages and currents arealso reduced, without introducing distortion, to save additional power.

[0018] Power consumption is the product of the RMS voltage and currentdrawn from battery 15. Hence, by reducing the RMS voltage to amplifier10, power consumption is reduced beyond that provided by prior art powerconsumption techniques. Because cellular telephones generally operate atless than full power most of time, using the invention shown in FIG. 1will extend the life of battery 15 significantly.

[0019] A matching network 24 (e.g., a resonant circuit) interfaces theoutput of amplifier 10 to a load RL. Load RL may be an antenna or otherload. An input signal generator 26 generates a modulated RF signal Vinin a conventional way and may include automatic gain control circuitry.

[0020]FIGS. 2-6 illustrate some of the techniques which may be used bycontroller 14 to detect the output power or desired output power ofamplifier 10 in order to suitably control regulator 12 to generate avariable Vdd for amplifier 10 or to control the bias settings inamplifier 10.

[0021] In FIG. 2, a power detector 30 is connected to the output ofpower amplifier 10 or to the output of the matching network 24, via acoupler 31, to generate a voltage at lead 32 related to the output powerof amplifier 10. Coupler 31 couples a small percentage of the outputsignal to the power detector 30. Power detectors are well known and maytake many forms. Controller 42 converts the signal on lead 32 into acontrol signal for regulator 12 for adjusting Vdd to optimize theefficiency of amplifier 10.

[0022] Controller 42 may be coupled to a feedback terminal 43 ofregulator 12, where the feedback signal Vfb has a predeterminedrelationship with the voltage on lead 32. Thus, controller 42 may simplybe a level shifter or suitable amplifier. By appropriate design of thepower detector 30, the feedback terminal 43 of regulator 12 may insteadbe directly connected to lead 32, so that the power detector 30 acts asthe controller. The relationship between the input of controller 42 andthe output of controller 42 is to be determined based upon theparticular regulator 12 and power amplifier 10 used.

[0023] Some cellular telephones and other wireless transceivers alreadyemploy an output power detector for another purpose, and, thus, thepresent invention may be easily incorporated into such devices.

[0024] Regulator 12 may be any conventional high-efficiency switchingregulator which provides an output voltage based upon a feedback signal,as is well-known in the art. In conventional voltage regulator circuits,the feedback terminal of a regulator is connected to a divided regulatedoutput voltage.

[0025]FIG. 3 illustrates a controller 50 which senses the output voltageVpa of amplifier 10 and essentially acts as a negative peak detector tooutput a voltage Vnp representative of the most negative output ofamplifier 10 over a period of time. The battery voltage Vbatt applied toterminal 52 slowly pulls up node 54 to the battery voltage throughresistor 56. Voltages applied to the cathode of diode 58 which are lowerthan one diode drop below the voltage at node 54 pull down the voltageat node 54 to approximately the most negative voltage applied toterminal 52 plus a diode drop. The selection of the resistor 56 valueand the capacitor 59 value determines the response of controller 50. TheRC time constant is preferably set so that there is no appreciablechange at node 54 from cycle to cycle.

[0026] The voltage at node 54 is applied to one input terminal of anamplifier 60, and a reference voltage 62 is applied to another inputterminal. The output of amplifier 60 is applied to the feedback terminalof regulator 12. In response, regulator 12 provides an operating voltageVdd to amplifier 10 so as to maintain the voltage at node 54 atapproximately Vref. If Vref is held fixed, then controller 50 acts toregulate the minimum voltage across the amplifier 10 outputtransistor(s) needed to avoid adverse distortion, thus optimizing theamplifier's efficiency at all output power levels. The technique of FIG.3 may be used to control the minimum voltage across the transistors inall stages of amplifier 10 (e.g., transistors Q1 and Q2 in FIG. 10). Forexample, with reference to FIG. 10, the minimum drain-source voltageacross transistors Q1 and Q2 to allow transistors Q1 and Q2 to operatein a linear region is regulated using the circuit of FIG. 3. A buffermay be needed between the output of amplifier 10 and the input ofcontroller 50 to avoid undue loading.

[0027]FIG. 4 illustrates a controller 70 for regulator 12 which receivesas its input a receive signal strength indication (RSSI), provided by aconventional RSSI circuit 72 which generates a voltage indicating thestrength of a received signal. The strength of the received signal is,in certain cases, indicative of the required power to be transmitted foradequate two-way communication. This is especially true when the remoteoriginating transmit power is known. The wireless transceiver mayalready contain a RSSI circuit 72 for a different purpose. A higher RSSIsignal thus indicates to controller 70 to provide a feedback signal toregulator 12 to lower the voltage Vdd to amplifier 10 to improve theefficiency of amplifier 10 at the lower output power.

[0028]FIG. 5 illustrates how an input into controller 76 may be thebaseband signal 78 which is mixed with the modulating RF carrier,generated by modulator 80, by multiplier 82. Since the output power ofamplifier 10 varies with the amplitude of the baseband signal 78,controller 76 may cause regulator 12 to modulate the voltage Vdd intoamplifier 10 in accordance with the baseband signal. The technique ofFIG. 5 is only applicable for forms of modulation which havenon-constant envelopes.

[0029] In another embodiment, shown in FIG. 6, controller 83 receivesits signal directly from the output of amplifier 10 or the matchingnetwork 24. Controller 83 converts this signal level into a controlsignal for regulator 12.

[0030] Other forms of controllers would be suitable depending upon thespecific transmitter to be controlled.

[0031]FIG. 7 illustrates a receiver 85 in a wireless transceiver whichreceives its operating voltage Vdd from regulator 12. Controller 87controls the output of regulator 12 to improve the efficiency ofreceiver 85 at lower received signal levels. A lower strength receivedsignal, detected by RSSI circuit 72, lowers the Vdd applied to receiver85 to optimize efficiency. Bias voltage/current levels may also beadjusted by controller 87 via line 88.

[0032]FIGS. 8 and 9 illustrate two types of simple switching regulators:FIG. 8 illustrates a buck type regulator 90, and FIG. 9 illustrates aboost type regulator 92. Such regulators may be used for regulator 12 inthe various figures. In such regulators, the duty cycle of the switch S1(typically a switching transistor) is controlled, where the duty cycleis directly proportional to the output voltage Vdd of the regulator. Aduty cycle controller 94 controls the switching of S1 based upon afeedback signal Vfb from any of the controllers shown in FIGS. 1-7. Areference voltage Vref is compared to the feedback signal by amplifier96 for adjusting the duty cycle of switch Si. An oscillator 98 providesthe switching frequency of switch S1. Those skilled in the art arefamiliar with the operations of the regulators of FIGS. 8 and 9. Aboost-buck regulator may also be used, which is typically a combinationof the circuits of FIGS. 8 and 9.

[0033]FIG. 10 illustrates one of the many appropriate types of poweramplifiers 10 which may be used with the present invention. A modulatedRF input signal from generator 26 is supplied through resistor R andcapacitor C1 to the input of a field effect transistor Q1. A variablebias voltage generator 106, controlled by controller 14 in FIG. 1,provides a bias voltage for operating transistor Q1 around a certainoperating. point. Inductor L1 and capacitor C1 form an input matchingnetwork for transistor Q1. The signal generated at the drain oftransistor Q1 is provided to the gate of transistor Q2, via DC blockingcapacitor C2, for further amplification. Inductor L2, inductor L3, andcapacitor C2 form a matching network between transistors Q1 and Q2.

[0034] The drain of transistor Q2 provides the output Vpa of amplifier10. A second variable bias voltage generator 108, controlled bycontroller 14 in FIG. 1, provides a bias voltage for operatingtransistor Q2 around a certain operating point. The drain of transistorQ2 is connected to a matching network 24 for appropriate resonant tuningto improve gain, lower the return loss, lower distortion, increaseoutput power, and increase efficiency. The matching network 24 consistsof inductor L4 connected between Vdd2 and transistor Q2, inductor L5,and capacitors C3 and C4. The voltage output Vout is then applied acrossa load RL (e.g., an antenna) for transmission.

[0035] The operating conditions of transistors Q1 and Q2 must be set sothat the voltage swings and/or drain currents of transistors Q1 and Q2are not distorted in an unacceptable way. The adjustable bias voltagesVbias1 and Vbias2 as well as voltages Vdd1 and Vdd2 are thereforedynamically controlled to avoid such distortion of the signals providedby transistors Q1 and Q2. Suitably controlling the operating conditionsusing the present invention results in less battery power being wastedthrough the various conduction paths.

[0036] The variable voltage sources (e.g., controllable regulators) usedfor sources 106 and 108 may be conventional. The particular biasvoltages needed at various output power levels are determined on acase-by-case basis depending upon the particular amplifier andapplication.

[0037] The controller 14 (FIG. 1) may control the output of regulator 12to set the Vdd1 and Vdd2 levels to be the same or different, dependingon the minimum voltage needed to operate transistors Q1 and Q2 at lowdistortion at a particular output power.

[0038] In the example shown in FIG. 10, transistors Q1 and Q2 aremetal-semiconductor field effect transistors (MESFETs).

[0039] A power amplifier using bipolar technology may also utilize thepresent invention, where the collector-emitter voltage Vce of theamplifier's transistor(s) is regulated to be a minimum needed to operatethe transistor(s) at all output levels without distortion. Such anamplifier may replace the MESFET transistors Q1 and Q2 in FIG. 10 withbipolar transistors. MOSFET transistors may also be used.

[0040] This technique of dynamically adjusting the operating conditionsin an amplifier may be applied to many forms of power amplifiers, andthe particular type of controller used will depend upon the method whichwill provide the most efficient use of battery power at a reasonablecost. Many of the circuits which generate the input to controller 14(FIG. 1) already exist in certain cellular telephones, such as the powerdetection circuit 30 of FIG. 2 and the RSSI circuit 72 of FIG. 4. Thepresent invention is not restricted to any particular switchingregulator (e.g., PWM, PFM), and a suitable regulator may also be anon-switching regulator, such as a linear regulator. However, switchingregulators are known to be highly efficient.

[0041] It is expected that the present invention will increase thebattery life of cellular telephones and other wireless transceivers byas much as 50k or more. In some applications, it is anticipated thatbattery life will be at least doubled using the present invention.

[0042] While particular embodiments of the present invention have beenshown and described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the appended claims areto encompass within their scope all such changes and modifications asfall within the true spirit and scope of this invention.

1-37. (Cancelled)
 38. A mobile wireless device comprising: an amplifiercoupled to receive a first signal, the first signal being amplified inthe amplifier, and to provide the amplified first signal to an antennaof the wireless device through an output matching network; a switchingvoltage regulator circuit having an input terminal coupled to receive aDC voltage provided by a battery, and an output voltage terminal thatsources a first variable voltage signal across terminals of a transistorof the amplifier; a bias voltage generator that generates a secondvariable DC voltage signal that is provided to an input of thetransistor; and a controller having an input terminal connected toreceive a first signal, wherein the first signal is sampled between theoutput of the amplifier and the antenna, the controller receives asecond signal based on said sampling, the controller provides a thirdsignal to the switching voltage regulator that determines the firstvariable voltage signal, and the controller provides a fourth signal tothe bias voltage generator that determines the second variable voltagesignal, the third and fourth signals being dependent on a value of thefirst signal.
 39. The mobile wireless device of claim 38, wherein thefirst signal is sampled between the output of the amplifier and theoutput matching network.
 40. The mobile wireless device of claim 38,wherein the first signal is sampled between the output matching networkand the antenna.
 41. A mobile wireless device comprising: an amplifiercoupled to receive a first signal, the first signal being amplified inthe amplifier, and to provide the amplified first signal to an antennaof the wireless device through an output matching network; a switchingvoltage regulator circuit having an input terminal coupled to receive aDC voltage provided by a battery, and an output voltage terminal thatsources a first variable voltage signal across terminals of a transistorof the amplifier; a bias circuit that generates a second variable DCvoltage signal that is provided to an input of the transistor; and acontroller, wherein the switching voltage regulator is coupled to anoutput of the controller, and receives a signal from the controller thatdetermines the first variable voltage signal, the controller determiningsaid signal based on a strength of a signal received by the mobilewireless device from another transmitter, and wherein the bias circuitis coupled to an output of the controller, and receives a signal fromthe controller that determines the second variable voltage signal, thecontroller determining said signal based on the strength of the signalreceived by the mobile wireless device from the other transmitter.